GEOLOGY OF GILES COUNTY, VIRGINIA 
375 
Mississippian and Pennsylvanian rocks were laid down in 
Giles County, but have been subsequently eroded. There is no 
direct evidence for making this assertion, but Pennsylvanian 
rocks are found on either side of the county, and since faulting 
has so raised the entire area that Shenandoah lime is in contact 
with Kimberling shales, there has been every opportunity for 
erosion to have removed these later Paleozoics. 
After this time, the uplift was rather steady and Giles County 
becomes a land mass. Folding and faulting were not pronounced 
in the Mesozoic, and by the end of this era a great peneplain had 
been reached. However, in Oligocene time upwarping began 
along the Appalachian axis and continued throughout the epoch. 
As a result, the stream gradients were increased and erosion 
began apace. As a result, the Tertiary Gravels were deposited in 
those areas where the stream currents were abruptly checked. 
The uplifts in the several periods of movement were continuous, 
but gradual, as is evidenced by the fact that the New River has 
been able to maintain its course through the ridges which are 
due to the hard layers. 
The rocks of Giles County suffered no close folding during 
the Paleozoic because, while unconformities can be found, the 
angular type is inconspicuous. There are no typical continental 
deposits in the county unless we except the Tertiary Gravels 
mentioned above. The Clinch has been regarded as a delta de- 
posit and its shape and lithologic character in many areas seem 
to confirm this view. Here, however, the presence of a marine 
fossil, (Lingula cuneata) as well as shaly layers indicates that 
the formation is at least semi-marine, and if it is a portion of a 
delta deposit, it is the extreme outer edge of such a formation. 
Mud cracks are common in many of the formations showing 
shallow seas, yet marine fossils are also found in these same hori- 
zons. Rapid changes of conditions are shown by the presence, in 
some places, of limestone breccias, as well as fissile shale partings 
in the great limestones. 
The chert in some of these limestones seems to be a surface 
feature, as deep quarries run out of the chert zone. The presence 
of chert everywhere in deep caverns may or may not be regarded 
as an additional proof of the surface character of the chert. 
Calcite is also secondary in these limestones and is regarded as 
Mesozoic or Tertiary in age, having formed everywhere in the 
